1. Field of the Invention
This invention relates to a pointer detection apparatus and a pointer detection method, and more particularly to a pointer detection apparatus and a pointer detection method wherein the position of a pointer is detected by an electrostatic coupling system.
2. Description of the Related Art
Conventionally, for the detection of the position of a pointer such as a finger or a pen for use with a touch panel or a like apparatus, various systems have been proposed such as, for example, a resistive film system, an electrostatic coupling system, and an electrostatic capacity system. In recent years, a pointer detection apparatus including the electrostatic coupling system, from among the various systems mentioned above, has been vigorously developed.
Electrostatic coupling systems are roughly divided into two types including a surface capacitive type and a projected capacitive type. An electrostatic coupling system of the surface capacitive type is applied, for example, in an ATM (Automated Teller Machine), and that of the projected capacitive type is applied, for example, in a portable telephone set. It is to be noted that, in both types, a variation of the electrostatic coupling state between a conductive film and a pointer such as a finger or an electrostatic pen is detected to detect the position of the pointer.
A pointer detection apparatus of the projected capacitive type electrostatic coupling system includes an electrode formed in a predetermined pattern, for example, on a transparent substrate or a transparent film and detects a variation of the electrostatic coupling state between a pointer and the electrode when the pointer approaches the electrode. For a pointer detection apparatus of the type described, various techniques for optimizing the configuration have been proposed and are disclosed, for example, in Japanese Patent Laid-Open Nos. HEI 5-224818, HEI 6-4213, HEI 7-141088, HEI 8-87369, HEI 8-179871, HEI 8-190453, HEI 8-241161, HEI 9-45184, 2000-76014, 2000-105645, 2000-112642, and HEI 10-161795.
Here, operation of a pointer detection apparatus of the cross point type electrostatic coupling system developed from the projected capacitive type electrostatic coupling system is described briefly with reference to the accompanying drawings. FIGS. 62A and 62B illustrate a general configuration of a sensor section and a position detection principle of a pointer detection apparatus of the cross point type electrostatic coupling system.
Referring to FIGS. 62A and 62B, a sensor section 300 includes a transmission conductor group 303 formed from a plurality of transmission conductors 304, and a reception conductor group 301 formed from a plurality of reception conductors 302. An insulating film is formed between the transmission conductor group 303 and the reception conductor group 301. The transmission conductors 304 extend in a predetermined direction indicated by an arrow mark X and are disposed in parallel to each other and in a spaced relationship by a predetermined distance from each other. The reception conductors 302 are in the form of a wire extending in a direction crossing the extension direction of the transmission conductors 304, that is, in the direction indicated by an arrow mark Y in FIG. 62A and are disposed in parallel to each other and in a spaced relationship at a predetermined distance from each other.
In the sensor section 300 having the configuration described above, a predetermined signal is supplied to a predetermined one of the transmission conductors 304 and a variation of current flowing to a cross point between the predetermined transmission conductors 304 and a reception conductor 302 is detected at each of the cross points of the predetermined transmission conductors 304 and the reception conductors 302. A system of detection just described is generally called cross point type electrostatic coupling system. At a position of the sensor section 300 at which a pointer 310 such as a finger is placed, current is shunted through the pointer 310 and varies. Therefore, the position of the pointer 310 can be detected by detecting a cross point at which current exhibits a variation. Further, in a pointer detection apparatus of the cross point type electrostatic coupling system, multipoint detection is possible because a plurality of cross points are provided on the sensor section 300 as seen in FIGS. 62A and 62B.
A principle of position detection of the cross point type electrostatic coupling system will now be described more particularly. Assume for example that a predetermined signal is supplied to the transmission conductor Y6 and a pointing position of the pointer 310 on the transmission conductor Y6 is detected as seen in FIG. 62A. When a signal is supplied to the transmission conductor Y6, the difference between currents flowing to the reception conductors X0 and X1 is detected through a differential amplifier 305. Then, after a predetermined interval of time, the reception conductors to be used for current difference detection are changed over from the reception conductors X0 and X1 to the reception conductors X1 and X2, and the current difference between the reception conductors X1 and X2 is detected. This operation is repeated up to the reception conductor XM.
Thereupon, a level variation of an output signal of the differential amplifier 305 at the position of each cross point on the transmission conductor Y6 is determined FIG. 62B illustrates a characteristic of the level variation. In FIG. 62B, the axis of abscissa indicates the distance from the reception conductor X0 to each reception conductor, that is, the position of each reception conductor, and the axis of ordinate indicates the level of an output signal of the differential amplifier 305, that is, an output value of the differential amplifier 305. In FIG. 62B, a broken line curve represents a characteristic of the level variation of the output signal of the differential amplifier 305 and a solid line curve represents a characteristic of the integration value of the output signal of the differential amplifier 305.
In the example illustrated in FIGS. 62A and 62B, since the pointer 310 is placed in proximity to cross points of the reception conductors X4 and XM-5 on the transmission conductor Y6, current flowing in proximity to the cross points varies. Therefore, in the example illustrated in FIG. 62B, the output signal of the differential amplifier 305 varies at corresponding positions in proximity to the cross points of the reception conductors X4 and XM-5 on the transmission conductor Y6, and the integration value of the output signal exhibits a low value, that is, a negative value. The position of the pointer 310 can be detected based on the variation of the integration value. In the conventional pointer detection apparatus, the detection described above is carried out while successively changing over between the transmission conductors, to be used for the detection, one by one.